This invention relates generally to a floating fish rearing system and more particularly to a system which provides for the rearing of fish, such as trout, in water bodies which under normal circumstances would not permit controlled rearing near the surface thereof due to water temperature and/or oxygen content.
The merits of fish culture in general, and salmonid culture in particular, are well-known.
The future bodes well for fish culture, since fish culture will invariably increase greatly as wild fish stocks are depleted, fish rearing techniques are improved, genetic manipulations of fish are perfected, and peoples' eating habits change toward animal species which have high feed conversion ratios.
Presently, salmon and trout are the most popular species of cultivated fish in the United States. These fish are principally reared for "wild" population replenishment and supplementation, but they are also increasingly reared for the supermarket. State and Federal hatcheries during 1973 collectively produced 216,000,000 coldwater fish weighing 22,000,000 lbs. while commercial U.S. production totaled about 16,000,000 lbs. California State Hatcheries alone produced 55,372,495 fish weighing 4,134,216 lbs. during 1972-73. Trout (primarily rainbow trout) account for about 70% of all fish produced. Virtually all State and Federal production is for release to the "wild" whereas 80% of commercial production is for direct sale to the market.
Fish consumption in the U.S. is 11.2 lbs. per capita, compared with 70 lbs. per capita in most Asian countries. Fish consumption per capita in the U.S. will increase an energy conservation practices take effect. Fish production costs per pound of protein are less than similar beef costs and should decrease significantly as fish culture techniques are improved. Low cost of such a quality food item will increase demand for fish. In addition, as people become more health conscious, this diet should include significantly greater quantities of fish, since fish have lower concentrations of saturated fats.
The most common prior art fish rearing techniques include land-based, long raceway systems which are supplied by water diverted from streams, springs, or water pumped from wells. However in most parts of the country economically feasible sites for such operations are either very limited or non-existent. Pond systems, similar to land-based raceways, are also used but are subject to the same cost limitations and also provide more difficulties for controlled rearing since the fish are not as controllably confined as with raceway systems.
Floating pens have also been used and are most applicable to moving water locations, especially salt water locations with a good tidal flush, and large rivers. Structural problems and problems of contamination and debris are limiting their present application. Also, recirculating systems which recycle most or all of the water have been used in the process of fish rearing. These latter systems generally use silos and may overcome many problems such as water shortages, temperature control and pollution effects of the discharged water. Thus far however these systems are too expensive to make fish rearing possible on a profitable basis.
The present invention overcomes the drawbacks of all of the above mentioned prior art devices and makes fish rearing possible in a relatively simple and profitable manner. Although the invention is primarily directed to trout culture in lakes, the principles thereof could also be used to rear other species in fresh or salt water.
One of the primary objects and advantages of the invention is good water temperature selection. With the present invention, it is possible to select the most desirable temperature found between the surface and maximum depth. Lake temperatures may range in the summer from 40.degree. F. at the bottom to 75.degree. F. at the surface in temperate lakes, and 55.degree. to 80.degree. F. in semi-tropical lakes such as those characteristic of many lower elevation California areas. Temperatures may be selected to accelerate or retard fish growth or to cause ripening of brood stock. With the present invention, it is possible to simultaneously have different water temperatures in different raceways.
A related advantage of the invention is an almost restricted geographical limitation. The system can be operated essentially any place in the U.S. which has a sufficient volume of deep, thermally stratified water. This greatly expands the range limitations of conventional raceways. It also makes use of the system possible in areas such as San Diego which has reservoirs suitable for the present inventive system but which has few small streams flowing year long and of the type suitable for more conventional trout rearing operations.
A further and important advantage of the present invention is the use of an unlimited water supply since the system recycles water within the lake. Conventional hatcheries have once through flow or they must use expensive means of reclaiming and reusing the water. Water shortages are one of the major limitations on conventional trout rearing. This situation will get worse as the demand for fish like trout increases and the usable water decreases due to other demands on its use. Furthermore, conventional hatcheries are faced with severe water shortages due to seasonal flows. Typically they are dependent on stream flows which are greatest in the spring and lowest in late summer when the water is most needed. It is also difficult to predict in advance what the situation will be in a given year.
A further advantage of the invention is good water flow control. With the present system, the rate of water flow can be adjusted to meet the needs at a given time.
Another advantage of the invention is debris free water since the water enters the system at a deep water zone. As a result less time is spent removing brush and other trash from raceway screens. Clogged screens could cause high fish mortality.
A further advantage of the invention is the minimal use of expensive land based operations. The system can be easily moved about the lake and additional raceways added to meet demand, etc.
A further advantage of the invention is a possible supply of free fish food in many applications. The deep waters of well oxygenated lakes normally have the greatest zooplankton concentrations during the daytime. The upwelled water may contain sufficient zooplankton concentrations to greatly reduce or eliminate feeding of the fish with prepared food such as dry pellets. This will reduce labor, food costs and pollution problems.
Other and further objects and advantages of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what are now considered to be the best modes contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.